In the conventional wireless communication system, the usable frequency band is assigned beforehand for each of a plurality of wireless communication systems, and each wireless communication system implements the wireless communication employing an assigned frequency band. However, the users of the wireless communication systems are on the increase at present, and it is difficult to treat the increasing number of users with only the assigned frequency band.
A method for using the frequency efficiently under this situation is provided in which each of a plurality of wireless communication systems has a private frequency band assigned to itself and a frequency band separate from this private frequency band is shared among the plurality of systems, whereby the frequency utilization efficiency, called as spectrum efficiency is improved (e.g., refer to JP-A-2003-333648).
There is disclosed in the document, JP-A-2003-333648, that a wireless communication system A with the increased communication traffic volume of the private frequency band issues a request for using the shared frequency band to another wireless communication system B employing the shared frequency band. Another wireless communication system B receiving the request yields up the shared frequency band to the wireless communication system A, if the communication traffic volume of its own private frequency band is small.
In this manner, the plurality of wireless communication systems employ the shared frequency band in accordance with the communication traffic volume of its own private frequency band, whereby the frequency is efficiently used.
However, in the configuration as described in the document, JP-A-2003-333648, if the communication traffic volume of the private frequency band for the wireless communication system B employing the shared frequency band is large, the wireless communication system B does not yield up the shared frequency band, and the wireless communication system A can not employ the shared frequency band. In this manner, there was a problem that if the communication traffic volume of the plurality of wireless communication systems increase, the wireless communication system that can not employ the shared frequency band has the lower throughput or the refusal of communication request. Further, even if the wireless communication system A employs the shared frequency band, the traffic can not be treated only with the private frequency band and the shared frequency band, when the communication traffic volume greatly increases, resulting in a problem that the lower throughput or the refusal of communication request occurs.